The Radiological Physics Center for the Collaborative Ocular Melanoma Study is being established to insure the correctness and consistency of radiation dosimetry for patients entered onto the Collaborative Ocular Melanoma Study (COMS). In conjunction with the COMS Radiation Therapy and Physics Committee, the Physics Center will develop specific guidelines for treatment of patients with radiation therapy, develop guidelines for monitoring compliance with this treatment protocol at all centers involved in COMS, and provide continued radiotherapy quality assurance for COMS. Quality assurance procedures for external beam radiotherapy are well developed and include dosimetry review visits by a Physics Center physicist to the participating institutions, mailed dosimeters, and review of individual patient treatment records. Quality assurance review of radioactive plaque therapy will be accomplished by development of standard plaque techniques, comparison of dosimetry calculations at participating institutions, review of institutions quality assurance procedures to verify the calibration of sources, and review of individual patients treatment records to verify that the stipulations of the protocol have been met. A physicist from this center will visit participating institutions who experience radiotherapy physics related problems. The Radiation Therapy Committee of the American Association of Physicists in Medicine will serve as the scientific advisory board for these activities. Knowledge gained will be communicated to the radiologic and opthamalogic communities.